The invention concerns a method for the galvanic deposition of smooth and ductile copper from acid copper baths, the metal content of which remains unchanged during the deposition.
Acid copper baths are customarily run with soluble copper anodes. These are hung in baskets in the bath in the form of wire bars, ingots or also as granulates or pieces, and deliver, with anodic connections corresponding to the quantity of current according to Faraday's Law, approximately 100% yield of copper ions in the electrolyte. In so doing it has been shown that it is significant to add small amounts of phosphorus to the copper so that the anodes, through formation of a uniform anode film, will dissolve better and display no passive spots.
Such copper baths, particularly with a content of organic thio compounds, find use predominantly for galvanic deposition of smooth and ductile copper. A preferred field of application is the building up of conductor paths on printed circuits.
Acid copper baths have, however, the disadvantage that in particular at high acid concentrations, besides the anodic dissolution of the anodes, also a chemical dissolution results, whereby the copper content in the bath is strongly increased. These baths must therefore be expensively controlled and from time to time thinned out, since this high copper concentration can give rise to a defective distribution of the deposited copper and even a crack in the printed circuit conductor paths with thermal stress.